Fix Claude 1-hour cache write pricing

[AgentSeal]

Summary

• Price 1-hour cache writes at 2x base input instead of the 5-minute 1.25x rate
• Read usage.cache_creation.ephemeral_5m/1h_input_tokens split from Claude JSONL
• Fall back to legacy all-at-5-minute-rate behavior for older sessions
• Bump daily cache to v6 so stale cost totals are recomputed

Based on #304 by @ozymandiashh. Closes #276.

Test plan

• 674/674 tests pass (6 new: pricing unit, integration, cache invalidation)
• Pricing math verified: 1.6x multiplier correct across all 7 Claude models
• All 18 existing calculateCost callers unaffected (new param is optional, defaults to 0)
• Non-Claude providers isolated, no cross-contamination
• Cache v5 backed up and recomputed, no data loss
• No security issues (NaN/negative/malformed data handled at both parser and cost layers)